In many power transmission mechanisms using a chain drive, an endless chain is in meshing engagement with a driving sprocket and with one or more driven sprockets. For example, in the timing drive of an automobile engine, a chain is driven by a crankshaft sprocket and drives one or more a camshaft sprockets. The chain is typically in sliding contact with one or more guide members including a movable tensioner lever and a fixed guide.
The chain is formed by articulably connecting a plurality of link plates which overlap one another along the length of the chain. Each link plate has a pair of connecting holes, and the plates are connected by insertion of connecting pins into the pin holes. At least some of the link plates have edges that come into sliding contact with a guide member.
In one well-known transmission chain, described in United States Patent Publication 2008/0020882, published Jan. 24, 2008, the shapes of the link plate edges which come into sliding contact with a guide member are in the form of convex curves so that the sliding contact area is reduced. At the same time, dynamic pressure generated in lubricant between the link plate edges and the guide surface reduces sliding contact resistance.
The above-mentioned well-known transmission chain is shown as chain 500 in FIG. 10. Edges 511 of the inner link plates 520 of the chain, and edges 521 of outer link plates 510, are the edges that come into sliding contact with a guide member (not shown). These edges are in the form of convex curves, and only the parts of the edges that protrude farthest from the line connecting the centers of the connecting pins 530 come, into sliding contact with the guide member. The sliding contact area is reduced and, at the same time, a wedge-shaped oil film is generated in wedge-shaped spaces in front of the areas of sliding contact so that a Couette's current is set up, causing dynamic pressure in a lubricant to reduce sliding contact resistance.
In chain 500, the link plates 510 and 520 are symmetrical in the sense that widest parts of the link plates are located midway between the pin holes with reference to the direction of chain travel. All of the link plates 510 and 520 come into sliding contact with a guide member at the same location on each link plate. These contact locations are unaffected by changes in chain tension, and a large amount of abrasive wear of the link plates occurs. Consequently, intrusion of powder, dust and the like produced by wear occurs, and vibration, contact noise and the like are liable to occur.
An object of the invention is to solve the above-mentioned problems, by providing a chain in which the sliding contact area is reduced, dynamic pressure is generated in the lubricant so that sliding contact resistance is reduced, and, at the same time, the locations on the link plate edges that contact a guide member are varied so abrasive wear is reduced, intrusion of wear powder, dust and the like is reduced, and vibration and contact noise are also reduced.